Circuits of various kinds are susceptible to a number of fault conditions. The types of faults a given circuit may experience depend at least in part on the type of circuit. For example, in an electrical circuit, damage to wiring and/or insulation may lead to electrical arcing between or within the wires, or between the wires and other structures. This is commonly referred to as an arc fault.
It is noted that many other types of faults, both in electrical circuits as well as pneumatic circuits, hydraulic circuits, and other circuits, are known. For exemplary purposes, arc faulting in an electrical circuit will be referred to herein as a specific example of a fault for purposes of description of the present invention. However, it is to be understood that the present invention is not limited to use with arc faults only, nor is it necessarily limited to use with electrical circuits only.
Returning to the specific example of arc faulting, the presence of an arc fault in an electrical circuit often is undesirable. Under some conditions, arc faulting potentially can pose a hazard to the circuit, to components thereof, to nearby materials, equipment, and persons, etc. Therefore, if arc faulting is detected within a circuit, it may be desirable to perform some action to oppose the fault, and/or to provide an indication that a fault has occurred.
Commonly, faults are opposed by interrupting the circuit that is experiencing the fault.
As a result, fault circuit interrupters are coming into use, for interrupting a circuit in the event that a fault is detected. However, conventional fault circuit interrupters are not entirely satisfactory.
For example, conventional circuit interrupters typically utilize only one lock, or interrupting mechanism, to open or break the circuit. With the lock closed, the circuit is closed; with the lock open, the circuit is open.
However, in some instances it also may be desirable to break an electrical circuit in the event that power to that circuit fails, or is shut off. Such a feature is increasingly required in commercial electrical circuits.
Conventional circuit interrupters either lack any means for opening the circuit when no power is applied, or use the same means as are used to open the circuit if and when a fault is detected.
The former approach, of course, does not provide the desired feature. The latter approach, however, may make it difficult to determine when and whether a fault has actually occurred.
For example, if the circuit interrupter interrupts the circuit, it may not be immediately apparent whether the circuit has been interrupted due to a fault or due to loss of power. Even if it is determined that the power has failed, there still is no positive indication as to whether a fault is or is not present as well.
Moreover, if the circuit experiences a fault, but the power then either fails or is deliberately terminated, there is no longer any clear evidence that the fault occurred, since the lock would have opened when the power failed regardless of whether a fault was present.
This may be of particular concern since, commonly, power to a circuit may be deliberately terminated when a fault is detected in order to avoid potential risks due to live power wires, etc.
Conversely, certain types of faults can, in certain circuits, cause power failures in and of themselves, for example by damaging a circuit component, producing a short that draws so much current that a circuit breaker or fuse opens, etc. In such an instance, it also may not be clear whether a power failure or a fault occurred, or if both occurred, which caused the other (if indeed one did cause the other).
Thus, the use of a single lock for both opening the circuit when power is lost and opening the circuit when a fault is detected can obscure the issue of whether either a power loss, a fault, or both are present.
In addition, with such a conventional arrangement, it may not always be necessary to take positive action in order to reset a circuit once the interrupter has opened the circuit. In at least some instances, the lock is designed so that if it is open when power is turned on, it closes by itself. Such a feature may in some circumstances be useful with regard to turning power on and off, in that if the circuit automatically opens when power is lost, it may be considered advantageous for the circuit to automatically close again when power returns.
However, if the same lock also responds to faults, the fault condition may cause recurrence simply by cycling the power on and off. Unless the matter is specifically investigated, under some circumstances the user may not even be aware that a fault occurred.